From the year 1059, who began electing Popes instead of powerful secular rulers?

Starting in 1059, it was the cardinals who began to assume the responsibility of electing the Pope, moving this power away from powerful secular rulers. This change was formalized at the Council of Rome, where Pope Nicholas II decreed that henceforth, only cardinals would have the authority to elect the Pope. This pivotal shift was significant in strengthening the Church's independence from political influence and helped to establish the role of the College of Cardinals as a key component in the governance of the Catholic Church. The move aimed to ensure that the selection of the Pope was based on theological and ecclesiastical considerations rather than political machinations, fostering a more spiritual and unified leadership within the Church.